Hermetic type compressor

ABSTRACT

A hermetic type compressor that includes a cylinder having a compression chamber with a cylinder head coupled to the cylinder to seal the compression chamber. A fastener fastened to the cylinder couples the cylinder head to the cylinder. A fastening hole is formed in the cylinder into which the fastener is received. A bush may be disposed between the fastener and fastener hole. The fastener may be made of a material having a thermal expansion coefficient less than that of the cylinder. Additionally, the bush may be made of a material having a thermal expansion coefficient greater than that of the cylinder.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. § 119 to Korean Patent Application No. 2005-57558, filed on Jun. 30, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hermetic type compressor, and more particularly, to a fixing bolt coupling structure for coupling a cylinder head with a cylinder.

2. Description of the Related Art

Generally, a hermetic type compressor is employed in the refrigeration cycle of a refrigerator, an air conditioner, or the like, and compresses refrigerant. The hermetic type compressor includes a compression part provided in a sealed container to compress the refrigerant and a driving part for supplying driving force to compress the refrigerant. The compression part and the driving part are installed using a frame.

According to the conventional hermetic type compressor, the cylinder may be formed with bolt fastening holes and fixing bolts screwed in the bolt fastening holes. The bolt fastening holes and the fixing bolts are sometimes made of different materials. Therefore, when the cylinder and the fixing bolts are heated by compression heat generated during the compression of the refrigerant, they thermally expand at different rates. For this reason, the fastening force between the bolt fastening holes and the fixing bolts is weakened.

In other words, when heat of the compression chamber in which the refrigerant is compressed or the refrigerant discharge chamber receiving the high-temperature and high-pressure refrigerant discharged from the compression chamber is transferred to the cylinder, the cylinder is expanded at a higher thermal expansion rate than the fixing bolts. As a result, distances between the inner circumferences of the bolt fastening holes and the outer circumferences of the fixing bolts increase, which causes the fastening force between the bolt fastening holes and the fixing bolts to decrease. Moreover, reduction of the fastening force of the fixing bolts reduces the coupling force of coupling the cylinder head with the cylinder so that the performance of the compressor is deteriorated because the compression chamber is not sufficiently sealed.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned problems, and an aspect of the invention is to provide a hermetic type compressor in which the fastening force of fixing bolts screwed in a cylinder to couple a cylinder head to the cylinder is prevented from deteriorating due to the compression heat of refrigerant.

To this end, one non-limiting aspect of the present invention provides a hermetic compressor, comprising a cylinder having a compression chamber; a cylinder head coupled to the cylinder to seal the compression chamber at least one fastener coupling the cylinder head to the cylinder, the at least one fastener being made at least in part of a material having a thermal expansion coefficient less than that of the cylinder at least one fastening hole, formed in the cylinder, configured to receive the at least one fastener and at least one bush configured to be disposed between the at least one fastener and the at least one fastening hole and made at least in part of a material having a thermal expansion coefficient greater than that of the cylinder.

Another non-limiting aspect of the present invention provides a hermetic type compressor that includes: a cylinder having a compression chamber; a cylinder head configured to be coupled with the cylinder to seal the compression chamber; and a plurality of fixing bolts configured to be fastened into a plurality of bolt fastening holes formed in the cylinder head to couple the cylinder head with the cylinder, wherein the plurality of fixing bolts are made at least in part of a material having a thermal expansion coefficient greater than a thermal expansion coefficient of the cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an elevational view of a hermetic type compressor in section according to a non-limiting embodiment of the present invention;

FIG. 2 is an exploded perspective view of a cylinder head and a valve device separated from a cylinder of the hermetic type compressor according to a non-limiting embodiment of the present invention;

FIG. 3 is an enlarged perspective view of the portion “A” of FIG. 2;

FIG. 4 is a partial elevational view in section of the cylinder head and the valve device assembled with the cylinder of the hermetic type compressor according to a non-limiting embodiment of the present invention and further illustrating a state before compression heat of refrigerant is transferred to the cylinder;

FIG. 5 is an enlarged elevational view in section of the cylinder head and the valve device assembled with the cylinder of the hermetic type compressor according to a non-limiting embodiment of the present invention and further illustrating the state in which compression heat of refrigerant has been transferred to the cylinder;

FIG. 6 is a partial perspective view illustrating non-limiting configurations of a bush and a bolt coupling hole of a hermetic type compressor according to another non-limiting embodiment of the present invention; and

FIG. 7 is a partial elevational view in section illustrating the coupling structure of a cylinder head and a cylinder in the hermetic type compressor according to another non-limiting embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the non-limiting embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals illustrate like elements.

By way of explanation, a hermetic compressor may include a compression part. This compression part may include a piston 9 connected to a rotation shaft 7 of the driving part for reciprocating, a cylinder 20 for forming a compression chamber in which the piston 9 is installed, a cylinder head 40 coupled with the cylinder 20 to seal the compression chamber 21 and having a refrigerant suction chamber 41 and a refrigerant discharge chamber 42 separated from each other, and a valve device 30 disposed between the cylinder 20 and the cylinder head 40 to intermit the flow of refrigerant introduced into the compression chamber 21 or discharged from the compression chamber to the refrigerant chamber.

The cylinder 20 may be integrally formed with a side of a frame 10 that is disposed in the lower side of the driving part to support the driving part. The frame 10 may be made of cast iron. When the driving part is driven by the above-described configuration and the rotation shaft 7 rotates, the piston 9 connected to the rotation shaft 7 through the connecting rod 8 reciprocates within the compression chamber 21. Thus, the refrigerant introduced into the compression chamber 21 from the outside of the sealed container via the refrigerant chamber is compressed in the compression chamber 21 and discharged out of the sealed container through the refrigerant discharge chamber. The process may be repeated so that the compression of the refrigerant is performed within the compressor. Meanwhile, the cylinder head 40 may be coupled with the cylinder 20 by plural fixing bolts 50 or like fasteners penetrating the cylinder head 40 and the valve device, which may be fastened to the cylinder 20 to seal the compression chamber 21. To fasten the fixing bolts 50 in the outer corners of the cylinder head 40 and the valve device, there may be provided through holes through which the fixing bolts 50 penetrate. In the ends of the cylinder 20 facing the valve device, a flange 23 may be provided such that bolt fixing holes 24 in which the fixing bolts 50 are screwed may be formed in the flange 23. By way of example, the fixing bolts may be made of Cr—Mo steel.

In more detail, a hermetic type compressor according to the first non-limiting embodiment of the present invention is shown in FIG. 1. In this non-limiting embodiment, the hermetic compressor may include a sealed container 1 having a refrigerant suction pipe 2 and a refrigerant discharge pipe 3, respectively installed in opposite sides thereof, and forming an external appearance of the hermetic type compressor, a compression part disposed in the sealed container 1 to compress refrigerant, and a driving part (not shown) for supplying a driving force to compress the refrigerant.

The driving part may include a stator 4 fixed to the upper outer side of a frame 10, a rotor 5 installed in the stator 4 to rotate due to the electrical interaction with the stator 4, and a rotation shaft 7. The rotation shaft 7 has an upper side fitted into the central portion of the rotor 5, a lower side supported by a journal bearing 6 installed in the central portion of the frame 10, and a lower end forming an eccentric part 7 a.

The compression part may include a piston 9 connected to the eccentric part 7 a of the rotation shaft 7 through a connecting rod 8, and configured to reciprocate during the rotation of the rotation shaft 7, the cylinder 20 for forming the compression chamber 21 in which the piston 9 may be installed, and the cylinder head 40 coupled with the cylinder 20 to seal the compression chamber 21. The cylinder head 40 may include refrigerant suction chamber 41 and refrigerant discharge chamber 42 separated from each other. Valve device 30 is disposed between the compression chamber 21 and the cylinder head 40 to intermit the flow of refrigerant introduced into the compression chamber 21 from the refrigerant suction chamber 41 or discharged from the compression chamber 21 to the refrigerant discharge chamber 42. The cylinder 20 may be integrally formed with a side of the frame 10.

Thus, due to the above-mentioned configuration, when the rotation shaft 7 rotates the rotor 5 due to the electric interaction between the stator 4 and the rotor 5 of the driving part, the piston 9 connected to the rotation shaft 7 through the connecting rod 8 reciprocates within the compression chamber 21. As a result, the refrigerant suctioned into the compression chamber 21 through the refrigerant suction pipe 2 and the refrigerant suction chamber 41 from the outside of the sealed container 1 is compressed in the compression chamber 21. The compressed refrigerant is discharged to the outside of the sealed container 1 through the refrigerant discharge chamber 42 and the refrigerant discharge pipe 3. By repeating the above processes, the compression of the refrigerant by the compressor is performed.

Moreover, as shown in FIG. 2, the cylinder head 40 may be coupled with the cylinder 20 to seal the compression chamber 21 using fixing bolts 50 made of, for example, Cr—Mo steel. The detailed configuration will be described as follows.

First, the cylinder 20 may be integrally formed with the frame 10 made of cast iron to form the compression chamber 21 therein, and may include a cylindrical part 22 extended from the side of the frame 10 and a rectangular flange 23 formed at the end of the cylindrical part 22 to be coupled with the cylinder head 40. The flange 23 may include bolt fastening holes 24 formed in the corners and is fastened with fixing bolts 50.

The valve device 30 may include a valve plate 41 having a suction hole 31 a formed in a central side to enable communication between the compression chamber 21 and the refrigerant suction chamber 41, a discharge hole (not shown) formed in another the other central side to enable communication between the compression chamber 21 and the refrigerant discharge chamber 42, and a discharge valve 31 b covering the discharge hole (not shown) from the outside of the discharge hole (not shown) to open and close the discharge hole (not shown), a suction valve 32 disposed between the valve plate 31 and the flange 22 of the cylinder 20 (which may further include a flap 32 a for opening and closing the suction hole 31 a), a first gasket 33 disposed between the suction valve 32 and the flange 22 to prevent the refrigerant from leaking, and a second gasket 34 disposed between the valve plate 31 and the cylinder head 40. In every component of the valve device 30 and the outer corners of the cylinder head 40, through holes 31 c, 32 b, 33 a, 34 a, and 43 may be formed to allow the fixing bolts 50 to penetrate them.

Thus, when the fixing bolts 50 penetrate in turn the through hole 43 of the cylinder head 40 and the through holes 34 a, 31 c, 32 b, and 33 a of the valve device 30 and are screwed into the bolt fastening holes 24 of the flange 22 of the cylinder 20, the cylinder head 40 may be coupled with the cylinder 20 by the fixing bolts 50 to seal the compression chamber 21.

Meanwhile, in the hermetic type compressor according to another non-limiting embodiment of the present invention, since the cylinder 20, the bolt fastening holes 24, and the fixing bolts 50 fastened in the bolt fastening holes 24 may be respectively made of different materials (such as, for example, cast iron and Cr—Mo steel), when the cylinder 20 and the fixing bolts 50 are heated due to the compression heat of the refrigerant generated during the compression of the refrigerant, the cylinder 20 and the fixing bolts 50 thermally expand at different rates so that the fastening force between the bolt fastening holes 24 and the fixing bolts 50 may be deteriorated. To overcome this difficulty, between the fixing bolts 50 and the bolt fastening holes 24, cylindrical bushes 50 made of material with thermal expansion coefficient greater than that of the cylinder 20 may be disposed. In this non-limiting embodiment, the bushes 60 may be made of copper.

For reference, the following table shows exemplary materials of the frame 10, the fixing bolts 50, and the bushes 60 employed in this non-limiting embodiment of the present invention, as well as the thermal expansion coefficients of the respective materials. Thermal Expansion Material Coefficient frame Cast iron 11.7 × 10⁻⁶ fixing bolts Cr—Mo steel 11.2 × 10⁻⁶ bushes copper 18.2 × 10⁻⁶

Heat from the compression chamber 21 or the refrigerant discharge chamber 42 may be transferred to the cylinder 20. When the cylinder made of cast iron and having a thermal expansion coefficient greater than that of the fixing bolts 50 (made of Cr—Mo steel) thermally expands at an expansion rate greater than that of the fixing bolts 50, predetermined gaps between the inner circumferences of the bolt fastening holes 24 and the outer circumferences of the fixing bolts 50 fastened therein are generated. However, the bushes 60 thermally expand between the bolt fastening holes 24 and the fixing bolts 50 at a rate greater than that of the cylinder 20 to fill the gaps between the bolt fastening holes 24 and the fixing bolts 50. Consequently, the fastening force between the bolt fastening holes 24 and the fixing bolts 50 can be prevented from deteriorating due to the compression heat of the refrigerant.

Although the bushes 60 may cover a whole length of the bolt fastening holes 24, in this non-limiting embodiment, as shown in FIGS. 3 and 4, the bushes 60 may cover only predetermined regions of the bolt fastening holes 24. where the fixing bolts 50 start to be inserted thereinto.

Thus, each bolt fastening hole 24 may include a large diameter part 24 a for forming a part of the bolt fastening hole 24 for supporting the outer circumference of the fixing bolt 50 through the bush 60 and a small diameter part 24 b having a smaller diameter than the large diameter part 24 a to form the bolt fastening hole 24 and to directly support the outer circumference of the fixing bolt 50. The large diameter part 24 a and the small diameter part may form a step in the bolt fastening hole 24. The ends of the bushes 60 installed in the large diameter parts 24 a may be supported between the steps of the bolt fastening holes 24 and the valve device 30.

Moreover, to secure fastening between the bushes 60 and the fixing bolts 50, the inner circumferences of the bushes 60 may be preferably supported by being screwed on the outer circumferences of the fixing bolts 50. To this end, the inner circumferences of the bushes 60 are formed with bush female threads 61. The bush female threads 61 succeed to small diameter female threads 25 b (FIG. 5) formed in the inner circumferences of the small diameter parts 24 b to form first female threads 24 c in association with the small diameter female threads 25 b. The fixing bolts 50 are fastened into the bolt fastening holes 24 such that first male threads 51 formed in the outer circumferences of the side screwed into the bolt fastening holes 24 are fastened with the first female threads 24 c.

The outer circumferences of the bushes 60 are screwed into the inner circumferences of the large diameter parts 24 a so that the bushes 60 are securely screwed into the bolt fastening holes 24 without using adhesive. To this end, bush male threads 62 are formed in the outer circumferences of the bushes 60 and large diameter female threads 25 b (FIG. 5) are formed in the inner circumferences of the large diameter parts 24 a.

In order to screw the bushes 60 into the large diameter parts 24 a, the bushes 60 may be rotated. In order to conveniently rotate the bushes 60 using a tool such as a screwdriver, preferably, screwdriver grooves 63 may be formed in the sides of the bushes 60 corresponding to the sides of the bolt fastening holes 24 where the fixing bolts 50 start to be inserted thereinto.

The coupling between the cylinder head 40 and the cylinder 20 of the hermetic type compressor according to a non-limiting embodiment of the present invention and operations thereof will be described as follows. First, the bushes 60 may be screwed into the large diameter parts 24 a of the bolt fastening holes 24 formed in the flange 23 of the cylinder. At that time, a screwdriver may be inserted into the screwdriver groove 63 formed in the end of the bush 60 so that the bush 60 is rotated by the screwdriver and the bush male thread 62 of the outer circumference of the bush 60 may be easily screwed on the large diameter female thread 25 b of the inner circumference of the large diameter part 24 a.

After installing the bushes 60, the components of the valve device 30 and the cylinder head 40 may be positioned at the outside of the flange 23 and the fixing bolts 50 penetrate in turn the through hole 43 of the cylinder head 40 and the through holes 34 a, 31 c, 32 b, and 33 a of the valve device 30, such that the fixing bolts 50 are fastened into the bolt fastening holes 24 formed in the flange 23 of the cylinder 20. Thus, the cylinder head 40 may be coupled with the cylinder 20.

At that time, the fixing bolts 50 may be fastened into the bolt fastening holes 24 such that the first male threads 51 formed in the outer circumferences facing the cylinder 20 may be fastened with the bush female threads 61 and the first female threads 24 c succeeding to the small diameter female threads 25 b.

Thus, in the hermetic type compressor according to another non-limiting embodiment of the present invention (as shown in FIG. 5) when heat from the compression chamber 21 or the refrigerant discharge chamber 42 is transferred to the cylinder 20, the cylinder 20 (made, for example, of cast iron) is thermally expanded at a thermal expansion rate greater than that of the fixing bolts 50 (made of, for example, Cr—Mo steel) during the compression of the refrigerant. However, since the copper bushes 60 have a thermal expansion coefficient greater than that of the cylinder 20, the copper bushes 60 are thermally expanded at a rate greater than that of the cylinder 20. Although gaps may be generated between the small diameter parts 24 b of the bolt fastening holes 24 and the fixing bolts 50, there may be no gap generated between the large diameter parts 24 a of the bolt fastening holes 24 and the fixing bolts 50 due to thermal expansion. Therefore, the fixing bolts 50 can be securely fastened into the bolt fastening holes 24 through the bushes 60. Moreover, the ends of the bushes 60 may be respectively supported by the steps of the bolt fastening holes 24 and the valve device so that the bushes 60 can be expanded toward only the outer circumferences and the inner circumferences.

Moreover, in the hermetic type compressor according to another non-limiting embodiment of the present invention, shown in FIG. 6, bushes 60′ may be fitted into the inner circumferences of large diameter parts 24 a′ of bolt fastening holes 24′. The outer circumferences of the bushes 60′ may have a polygonal shape to prevent the bushes 60′ screwed into the large diameter parts 24 a′ from rotating during the fastening of the fixing bolts 50. Preferably, the inner circumferences of the large diameter parts 24 a′ where the bushes 60′ may be installed may have a polygonal shape corresponding to the outer circumferences of the bushes 60′.

The bushes 60′ may also be made of copper (or another material) having a thermal expansion coefficient greater than that of the cylinder 20. Bush female threads 61′ may be formed in the inner circumferences of the bushes 60′ to be screwed with the fixing bolts 50 such that the same operation and effect as those of the first non-limiting embodiment are exhibited.

In a hermetic type compressor according to still another non-limiting embodiment of the present invention (shown in FIG. 7), the bushes 60 and 60′ may be omitted and fixing bolts 50″, which may be screwed into bolt fastening holes 24″ may be made of a material having a thermal expansion coefficient greater than that of the cylinder 20 to prevent the fastening force between the fixing bolts 50″ and the bolt fastening holes 24″ from deteriorating due to the compression heat of the refrigerant.

In other words, in this non-limiting embodiment of the present invention, bushes 60 and 60′ may be omitted between the bolt fastening holes 24″ formed in the cylinder and the fixing bolts 50″, and the bolt fastening holes 24″ may have uniform inner diameters between the ends thereof without steps. In order to couple the cylinder head 40 with the cylinder 20, the fixing bolts 50″, which may be fastened into the bolt fastening holes 24″, may be made of copper or an alloy containing copper (as non-limiting examples) to have a thermal expansion coefficient greater than that of the cylinder 20.

Thus, in the hermetic type compressor according to this non-limiting embodiment of the present invention, when first female threads 24 c″ of the bolt fastening holes 24″ are fastened with first male threads 51″ of the fixing bolts 50″ and the compression heat of the refrigerant is transferred to the cylinder 20, since the fixing bolts 50″ are thermally expanded at a rate greater than that of the cylinder 20, although the separate component such as bushes 60 and 60′ may be eliminated, there is no gap between the bolt fastening holes 24 and 24′ and the fixing bolts 50″ so that fixing bolts 50″ can be securely fastened into the bolt fastening holes 24″.

The hermetic type compressor of the non-limiting embodiments described above has advantages such that bushes, which may be made of material having a thermal expansion coefficient greater than that of the cylinder, may be installed between the bolt fastening holes formed in the cylinder, and the fixing bolts, which may be fastened into the bolt fastening holes to couple the cylinder head with the cylinder. Additionally or alternatively, the fixing bolts, fastened into the bolt fastening holes, may be made of a material having a thermal expansion coefficient greater than that of the cylinder, so that the fixing bolts can be securely fastened into the bolt fastening holes even though the cylinder and the fixing bolts are thermally expanded at different rates. As a result, deterioration of the sealing of the compression chamber due to the compression heat of the refrigerant and deterioration of the performance of the compressor can be prevented.

Although a few non-limiting embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. 

1. A hermetic compressor, comprising: a cylinder having a compression chamber; a cylinder head coupled to the cylinder to seal the compression chamber; at least one fastener coupling the cylinder head to the cylinder, the at least one fastener being made at least in part of a material having a thermal expansion coefficient less than that of the cylinder; at least one fastening hole, formed in the cylinder, configured to receive the at least one fastener; and at least one bush configured to be disposed between the at least one fastener and the at least one fastening hole and made at least in part of a material having a thermal expansion coefficient greater than that of the cylinder.
 2. The hermetic compressor according to claim 1, wherein an inner circumference of the at least one bush is threaded onto the at least one fastener.
 3. The hermetic compressor according to claim 2, wherein an outer circumference of the at least one bush is threaded into an inner circumference of the at least one fastening hole.
 4. The hermetic compressor according to claim 2, wherein an outer circumference of the at least one bush is received in an inner circumference of the at least one fastening hole.
 5. The hermetic compressor according to claim 1, wherein an outer circumference of the at least one bush is received in an inner circumference of the at least one fastening hole.
 6. The hermetic compressor according to claim 5, wherein the outer circumference of the at least one bush has a polygonal shape, and an inner circumference of the at least one fastening hole into which the at least one bush is threaded has a shape corresponding to the polygonal shape of the outer circumference of the at least one bush.
 7. The hermetic compressor as claimed in claim 1, wherein an outer circumference of the at least one bush is threaded into an inner circumference of the at least one fastening hole.
 8. The hermetic compressor as claimed in claim 7, wherein: the at least one bush is positioned in a side of the at least one fastening hole at an insertion point of the at least one fastener, and the at least one bush further includes at least one groove formed in at least one side thereof corresponding to the side of the at least one fastening hole.
 9. The hermetic compressor as claimed in claim 1, wherein: the at least one bush is installed in a side of the at least one fastening hole at an insertion point of the at least one fastener, and at least a portion of the at least one fastening hole includes at least first and second diameters, the first diameter being located where the at least one bush is installed and the second diameter being located inside the first diameter to form at least one step therebetween, and the first diameter is larger than the second diameter.
 10. The hermetic compressor as claimed in claim 1, wherein: the cylinder is made at least in part of cast iron, the at least one fastener is made at least in part of Cr—Mo steel, and the at least one bush is made at least in part of copper.
 11. A hermetic compressor, comprising: a cylinder having a compression chamber; a cylinder head configured to be coupled to the cylinder to seal the compression chamber; and a plurality of fixing bolts configured to be fastened into a plurality of bolt fastening holes formed in the cylinder head to couple the cylinder head to the cylinder, wherein the plurality of fixing bolts are made at least in part of a material having a thermal expansion coefficient greater than a thermal expansion coefficient of the cylinder.
 12. A hermetic compressor, comprising: a cylinder including a compression chamber; a cylinder head configured to be coupled to the cylinder; at least one fixing bolt configured to be attached to the cylinder to couple the cylinder head to the cylinder; at least one bolt fastening hole configured to receive the at least one fixing bolt; and at least one bush configured to be disposed between the at least one fixing bolt and the at least one bolt fastening hole.
 13. The hermetic compressor according to claim 12, wherein the at least one bush is comprised at least in part of a material having a thermal expansion coefficient greater than a thermal expansion coefficient of the cylinder.
 14. The hermetic compressor according to claim 12, wherein an inner circumference of the at least one bush is configured to be attached to an outer circumference of the at least one fixing bolt.
 15. The hermetic compressor according to claim 14, wherein an outer circumference of the at least one bush is configured to be attached to an inner circumference of the at least one bolt fastening hole.
 16. The hermetic compressor according to claim 12, wherein an outer circumference of the at least one bush is configured to be attached to an inner circumference of the at least one bolt fastening hole.
 17. The hermetic compressor according to claim 12, wherein a surface of the at least one bush has a polygonal shape.
 18. The hermetic compressor according to claim 17, wherein an inner surface of the at least one bolt fastening hole corresponds to the polygonal shape of the at least one bush.
 19. The hermetic compressor according to claim 12, wherein the at least one bolt fastening hole includes at least a first diameter and a second diameter, the first diameter being larger than the second diameter and positioned to receive the at least one bush.
 20. The hermetic compressor according to claim 19, wherein the second diameter is positioned inside the first diameter to form a step. 